Method of treating wet paint spray booth

ABSTRACT

In a method of treating a wet paint spray booth, the sepiolite alone or further accompanying the cationic polymer or the amphoteric metal compound is added. The wet paint spray booth treating agent and a method of treating a wet paint spray booth improve the effect of reduction in tackiness and decrease the load of agents to prevent the corrosion of furnishings. The sepiolite is a fibrous mineral containing chain structures having lots of micropores so that the sepiolite can reduce the tackiness of the paint due to reaction with the particles of the paint in such a manner to adsorb the particles in the micropores thereof. Since both the particles of the paint and the particles of the sepiolite are negatively charged, when the cationic polymer or the amphoteric metal compound is added in combination with the sepiolite, the electrical repulsion is reduced so that the particles of the paint become easy to be adsorbed to improve the effect of the reduction in the tackiness.

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional patent application of Ser. No. 09/466,806 filed onDec. 20, 1999 pending.

FIELD OF THE INVENTION

This invention relates to method of treating a wet paint spray booth.Particularly, this invention relates to a method of treating a wet paintspray booth with using a wet paint spray booth treating agent fordiminishing tackiness of paint in circulating water to be sprayed forcollecting the surplus paint and preventing the paint from adhering andfixing to an interior of the wet paint spray booth.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

In a painting process of an automotive industry, yield of paint sprayedto an automobile body is generally from 60 to 80% and 40 to 20% of thesprayed paint constitutes a surplus paint to be removed in a subsequentprocess. The surplus paint sprayed excessively is usually collected in awet paint spray booth by water washing and the washing water iscirculated for re-use.

In the wet paint spray booth, since the surplus paint collected in thewashing water has high tackiness, it adheres to a water-film panel, apiping system and a nozzle, and seriously degrades the efficiency ofwater washing. Moreover, the greater part of the surplus paint settlesto the bottom of the booth pit and the bottom of the circulation pit inthe spray booth, and the settled paint hardens into a rubbery state withelapse of time to take much time and labor for removal thereof.

For the solution of problems described above, a paint spray boothtreating agent as follows has been be added to the washing water:

1) alkali including NaOH or KOH

2) amphoteric metal salts including Zn salt

3) cationic polymers and metal salts, and

4) bentonite (montmorillonite, hectorite)

It is known that sepiolite is added to waste water including oilymatters and then the water is subjected to solid-liquid separation.However it is unknown to add sepiolite to the wet paint spray boothtreating agent.

Among the conventional wet paint spray booth treating agents mentionedabove, the effect of the alkalis for the reduction in the tackiness isnot enough. The amphoteric metal salts and the cationic polymers requireto be added in large amounts so that concentration of the salts isincreased to cause corrosion of materials, The effect of the bentonitefor the reduction in the tackiness is not enough so that a large amountof the cationic polymer is required to be added simultaneously.

Japanese patent publication 10-140045 discloses a paint compositioncapable of removing a toxic substance from a coated article. The paintcomposition contains a powdery or finely particular activated carbon andat least one kind of an activated carbon to which a toxic substanceremover is stuck such as an amine compound or titanium oxide and apowdery or finely particular porous material such as sepiolite orzeolite. W093/02147 (entered into Japanese phase and published as Tokuhyohei 6-509371) discloses an agent for removing tackiness of paintwhich comprises an inorganic aluminum compound and an organic polymercomprising a quaternary nitrogen atom.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the present invention to solve conventional problemsdescribed above and to provide a method of treating a wet paint spraybooth with using a wet paint spray booth treating agent which caneffectively reduce the tackiness and decrease the load of the agents sothat corrosion is prevented.

The wet paint spray booth treating agent of the present inventioncomprises sepiolite.

The wet paint spray booth treating agent of the present invention mayfurther comprise at least one of cationic polymer and amphoteric metalcompound.

In the method of treating a wet paint spray booth of the presentinvention, sepiolite and at least one of the cationic polymer andamphoteric metal compound are added into circulating water of the wetpaint spray booth.

Details of the effect of the wet paint spray booth treating agent of thepresent invention for the reduction in the tackiness is supposed asfollows.

The sepiolite is water-containing magnesium silicate having a chemicalformura Mg₈Si₁₂O₃₀(OH)₄(OH₂)₄.8H₂O. The sepiolite is a fibrous mineralcontaining chain structures having lots of micropores so that thesepiolite can reduce the tackiness of the paint due to adsorption of thepaint particles into the micropores thereof.

Since both the particles of the paint and the particles of the sepioliteare negatively charged, when the cationic polymer or the amphotericmetal compound is used in combination with the sepiolite, the electricalrepulsion is reduced so that the paint particles become easy to beadsorbed to the sepiolite particles whereby reducing the tackiness ofthe paint particles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional view illustrating a test deviceused in examples.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in more detail.

In the present invention, sepiolite to be used may be a naturallyproduced clay mineral. The natural sepiolite may be refined which iscommercially available. From the view point of the effect of thereduction in the tackiness, particles of the sepiolite is preferablyfibrous to have a fiber length of less than 50 μm, particularly lessthan 10 μm.

The cationic polymer to be added with the sepiolite may have a molarweight of more than 1000, preferably in a range of thousands to hundredsthousands. The cationic polymer may be at least one ofdimethyldiallylammonium chloride, the condensate of alkylamine andepichlorohydrin, ethyleneimine, the condensate of alkylene dichlorideand polyalkylenepolyamine, the condensate of dicyandiamide and formalin,DAM (homopolymer or copolymer of dimethylaminoethylmethacrylate) and thelike.

The amphoteric metal compound, may be at least one of PAC (polyaluminumchloride), aluminum sulfate, polyaluminum hydroxychloride, aluminumcompound including pseudoboehmite alumina sol (AlO(OH)), iron compoundincluding ferric chloride and zinc compound including zinc chloride andthe like.

The type of the wet paint spray booth being applied with the wet paintspray booth treating agent of the present invention is not restricted,i.e. it may be either dispersion type or floating type. The sepiolitealone or further in combination with at least one of the cationicpolymer and the amphoteric metal compound may be added into thecirculating water to become a predetermined concentration. The treatingagent adheres to the surplus paint to reduce the tackiness thereof, andthe agent is discharged out of the circulating system along with thesludge of the paint during the sludge separating process. The agent issupplemented to the system in an amount which is discharged.

As adding amount of the sepiolite becomes larger, the particles of thepaint become finer to improve the effect of the reduction of thetackiness. The concentration of the sepiolite in the circulating wateris preferable to be 1 ppm or more, particularly 10 ppm or more, moreparticularly 500 ppm or more.

The preferable concentration of the sepiolite depends on the type of thewet paint spray booth as follows.

1) When the wet paint spray booth is of the dispersion type where thewet paint spray booth employs the circulating water comprisinghomogeneously suspended sludge and a part of which is separated by aseparator such as a centrifugal dehydrator to recover SS (suspendedsubstances).

In this case, the wet paint spray booth treating agent of the presentinvention is preferable to be added to the circulating water so that theconcentration of the sepiolite becomes 50 ppm or more preferably between100 and 500 ppm to reduce the tackiness and to disperse the particles.In this case, since the sepiolite adheres to the surplus paint anddischarged accompanied with SS recovered by the separator, the sepioliteis preferable to be supplemented by continuous injection or batchinjection in an amount of 0.1 ppm by weight or more, particularly in arange of 1 to 5% by weight based on the weight of the solid content ofthe surplus paint which is fed to the circulating water.

When the wet paint spray booth treating agent of the present inventionis applied to the wet paint spray booth of the dispersion type, thesludge is effectively recovered and the water content of the recoveredsludge becomes sufficiently low.

2) When the wet paint spray booth is of the floating type.

The wet paint spray booth of the floating type allows the circulatingwater to have a little more tackiness than that of the dispersion type.The sepiolite is accordingly preferable to be added so that theconcentration thereof is 10 ppm or more, particularly in a range of 50to 200 ppm in the circulating water.

In this case, the sepiolite is preferable to be supplemented bycontinuous injection or batch injection in an amount of 0.1 ppm byweight or more, particularly in a range of 0.5 to 2% by weight based onthe weight of the solid content of the surplus paint which is fed to thecirculating water.

When the cationic polymer is used in combination with the sepiolite, thecationic polymer is preferable to be added in an amount expressed asactive principle of 0.01 to 20% by weight, particularly 0.5 to 10% byweight based on the amount of the sepiolite. The polymer is preferableto be comprised in such a manner to take the colloidal equivalent as0.001 to 1 meq/liter to the circulating water, particularly as 0.002 to0.5 meq/liter to the circulating water.

When the cationic polymer is added in an amount below the aforementionedrange, the effect obtained by combination with the sepiolite is notenough. When the cationic polymer is added in an amount exceeding theaforementioned range, the effect of the reduction in the tackiness ofthe paint becomes poor.

When an amphoteric metal compound is used in combination with thesepiolite, the amphoteric metal compound is preferable to be added in anamount expressed as the metal oxide of 0.01 to 10% by weight,particularly 1 to 10% by weight based on the amount of the sepiolite.

When the amphoteric metal compound is added in an amount below theaforementioned range, the effect obtained by combination with thesepiolite becomes not enough. When the amphoteric metal compound isadded in an amount exceeding the aforementioned range, the systemincluding the booth and pipes becomes susceptible to corrosion becauseof the rise in strength of the salts in the circulating water.

The way of adding the sepiolite is not restricted, i.e. the sepiolitemay be added in either form of the powder as it is or the suspensioncontaining about 0.1 to 10 wt. % sepiolite.

When both of the cationic polymer and the sepiolite are added, they maybe added either separately or in the form of the mixture. When thecationic polymer and the sepiolite are mixed each other in advance to beadded to the circulating water, it is preferable that the sepiolite isfirstly incorporated in a certain volume of water and then, after 1minute or more, preferably 20 to 30 minutes elapsed and after thesepiolite is sufficiently dispersed to increase the tackiness, thecationic polymer is added to prepare the mixed liquid. While, when thecationic polymer is firstly added into the liquid and then the sepioliteis added, the resulting liquid is generally poor in the effect of thereduction in the tackiness of the circulating water.

When both of the sepiolite and the amphoteric metal compound are addedto the circulating water, they are preferable to be added separately.When the mixture of the sepiolite and the amphoteric metal compoundwhich are mixed in advance each other is added, the effect of thereduction in the tackiness is low.

All of the sepiolite, the cationic polymer and the amphoteric metalcompound may be added to the circulating water.

In the present invention, besides the sepiolite, the cationic polymerand the amphoteric metal compound, many kinds of polymers having a largemolar weight including anionic and nonionic polymers, for examplepolyacrylamide and its partial hydrolyzate, acrylic polymer andmethacrylic polymer etc. may be added to the circulating water toenhance the aggregation and the solid-liquid separation of the sludge ofthe paint.

An alkali agent including sodium hydroxide, sodium carbonate, potassiumhydroxide or potassium carbonate may also be added to the circulatingwater to neutralize the circulating water and prevent corrosion of thesystem.

Examples and Comparative Examples

The present invention will now be described more specifically referringto examples and comparative examples but the present invention is notlimited to the following examples.

Examples 1 through 7, Comparative Examples 1 through 6

Using a test device shown in FIG. 1, effects for each kind of agentswere tested.

In FIG. 1, a reference numeral 1 designates a pit, 2 is a water filmplate, 3 is a circulating water pipe line having a circulating waterpump P, 4 is an exhaust cylinder having an exhaust blower 4A and W is awater level. 5 is a spray gun disposed above the water film plate 2 forblowing the paint. 6 is an agent adding section.

Tests were conducted by using the illustrated washing device having awashing water capacity of 50 liters wherein the circulating water flowedat a rate of 100 liter/min. The washing water was prepared by adding theagents shown in Table 1 in amounts as shown in Table 1. The tests werecarried out in such a way that intercoating materials used in theautomotive factories were blown at a rate of 15 g/min for 2 minutes fromthe spray gun 5 and, then, touched with fingers to evaluate thetackiness of the paint based on the following criteria. The results ofthe evaluation are shown in Table 1.

Criteria

X: Identical with the raw paint, easy to adhere to the finger

Δ: Slightly reduced in the tackiness as compared with the raw paint,less easy to adhere to the finger

◯: Practically eliminated in the tackiness, free of adhesion to thefinger

TABLE 1 Agents_(*1) Amphoteric Clay mineral Cationic polymer metalcompound Kind*₂ Amount Kind*₃ Amount Kind Amount Evaluation Example 1Sepiolite 200 — 0 — 0 Δ 2 Sepiolite 200 — 0 PAC 1(0.5) Δ˜◯ 3 Sepiolite200 — 0 PAC 2(1) ◯ 4 Sepiolite 200 A 1(0.5) — 0 Δ˜◯ 5 Sepiolite 200 A2(1) — 0 ◯ 6 Sepiolite 200 B 1.5(0.75) — 0 Δ˜◯ 7 Sepiolite 200 B 3(1.5)— 0 ◯ Comparative 1 Bentonite 200 — 0 — 0 X Example 2 Bentonite 200 — 0PAC 2(1) X 3 Bentonite 200 A 4(2) — 0 Δ 4 —  0 — 0 PAC 15  X 5 —  0 A15  — 0 X 6 —  0 B 15  — 0 X *₁: The additive amount denotes theconcentration (mg/liter) of the active principle in the circulatingwater. The amphoteric metal compound is expressed as Al₂O₃. The amountbetween parentheses such as (1), (0.75) or (0.5) denotes a percentage(%) of the amount of the active principle based on the amount of theclay mineral. *₂: The sepiolite is Miraclay ® P-80V of Ohmi Mining Co.Ltd., having a fiber length of less than 2 μm. The bentonite isNeokunibond (trade mark) of Kunimi Co. Ltd. *₃: The polymer “A” isZeta-ace ® C301 of Kurita Water Industries Ltd., consisting of acondensation of alkylamine and epichlorohydrin. The polymer “B” iskurifix ® CL 611 of Kurita Water Industries Ltd., consisting of acondensation of alkylene dichloride and polyalkylenepolyamine.

As apparent from the above results, the wet paint spray booth treatingagent and the method of the treating a wet paint spray booth accordingto the present invention can obtain the remarkable effect of thereduction in the tackiness without the corrosion of the system.

Therefore by the treating agent and the treating method according to thepresent invention,

1) clogging in the nozzle due to the deposition of the paint to thepiping system or the like can be prevented to maintain the water washingefficiency at a satisfactory level and facilitate the maintenance.

2) deterioration of the working environment by the clogging in the gasdischarge system or the like can be prevented.

3) the paint sludge which deposits or floats in the booth pit or thelike is not easily solidified and can be removed readily.

4) cleaning liquid waste can easily be put to solid-liquid separationand the waste water can be treated easily.

5) solids in the washing water after use can be separated and removed ata high separating efficiency to maintain the clarity of the circulatingwashing water at a high level.

Then, treatment for the paint booth can be conducted with an extremeindustrial advantage.

Especially, the combination of the sepiolite and the cationic polymer orthe amphoteric metal compound can exceedingly improve the effect of thereduction in the tackiness. In this case, a very small amount of thecationic polymer or the amphoteric metal compound is sufficient so thatthe rise of strength of the salts can be restrained to prevent thecorrosion of the system.

What is claimed is:
 1. A method of treating a wet paint spray boothcomprising a step of adding sepiolite to circulating water for the wetpaint spray booth.
 2. A method of treating a wet paint spray booth asclaimed in claim 1, wherein cationic polymer is further added to thecirculating water.
 3. A method of treating a wet paint spray booth asclaimed in claim 1, wherein amphoteric metal compound is further addedto the circulating water.
 4. A method of treating a wet paint spraybooth as claimed in claim 1, wherein the wet paint spray booth is adispersion wet paint spray booth, and the concentration of the sepiolitein the circulating water is equal to or more than 50 ppm.
 5. A method oftreating a wet paint spray booth as claimed in claim 4, wherein theconcentration of the sepiolite in the circulating water is in a range of100 to 500 ppm.
 6. A method of treating a wet paint spray booth asclaimed in claim 1, wherein the wet paint spray booth is a dispersionwet paint spray booth, and the adding rate of the sepiolite based on theweight of solids content of surplus paint is equal to or more than 0.1%by weight.
 7. A method of treating a wet paint spray booth as claimed inclaim 6, wherein the adding rate of the sepiolite based on the weight ofsolids content of the surplus paint is in a range of 1 to 5% by weight.8. A method of treating a wet paint spray booth as claimed in claim 1,wherein the wet paint spray booth is a floating wet paint spray boothand the concentration of the sepiolite in the circulating water is equalto or more than 10 ppm.
 9. A method of treating a wet paint spray boothas claimed in claim 8, wherein the concentration of the sepiolite in thecirculating water is in a range of 50 to 200 ppm.
 10. A method oftreating a wet paint spray booth as claimed in claim 1, wherein the wetpaint spray booth is of a floating type, and the adding rate of thesepiolite based on the weight of solids content of surplus paint isequal to or more than 0.1% by weight.
 11. A method of treating a wetpaint spray booth as claimed in claim 10, wherein the adding rate of thesepiolite based on the weight of solids content of the surplus paint isin a range of 0.5 to 2% by weight.
 12. A method of treating a wet paintspray booth as claimed in claim 2, wherein the rate of the cationicpolymer to the sepiolite is in a range of 0.01 to 20% by weight whenexpressed as an active principle.
 13. A method of treating a wet paintspray booth as claimed in claim 2, wherein the rate of the cationicpolymer to the sepiolite is in a range of 0.5 to 10% by weight whenexpressed as an active principle.
 14. A method of treating a wet paintspray booth as claimed in claim 2, wherein the cationic polymer is addedin such a manner that a colloid value of the colloid equivalent falls ina range of 0.001 to 1 meq/liter.
 15. A method of treating a wet paintspray booth as claimed in claim 2, wherein the cationic polymer is addedin such a manner that a value of the colloid equivalent falls in a rangeof 0.002 to 0.5 meq/liter.
 16. A method of treating a wet paint spraybooth as claimed in claim 3, wherein the rate of the amphoteric metalcompound added to the sepiolite is in a range of 0.01 to 10% by weightwhen expressed as a metal oxide, based on the amount of the sepiolite.17. A method of treating a wet paint spray booth as claimed in claim 3,wherein the rate of the amphoteric metal compound added to the sepioliteis in a range of 1 to 10% by weight when expressed as a metal oxide,based on the amount of the sepiolite.
 18. A method of treating a wetpaint spray booth as claimed in claim 2, wherein the sepiolite and thecationic polymer are mixed in advance to be added to the circulatingwater, and wherein the sepiolite is firstly dispersed in a certainvolume of water and then the cationic polymer is supplied thereinto toprepare a liquid, and the liquid is added to the circulating water. 19.A method of treating a wet paint spray booth as claimed in claim 3,wherein the sepiolite and the amphoteric metal compound are separatelyadded to the circulating water.